New IISc research offers to detect glucose through painless photoacoustics

At present, blood glucose is usually measured using invasive methods involving pricking a small needle in the skin.
| Photo Credit: Photo for representation only

A new study by researchers at the Indian Institute of Science (IISc.) has offered an alternative to pricking a needle into the skin to detect blood glucose level in people suffering from diabetes.

According to IISc, “Blood glucose is usually measured using invasive methods involving pricking a small needle in the skin. But people suffering from diabetes have to test their glucose levels many times in a day. This repeated use of needles is inconvenient, and can increase the risk of potential infections.”

Researchers in the Department of Instrumentation and Applied Physics (IAP) have offered an alternative solution via a technique called photoacoustic sensing.

In this technique, when a laser beam is shone on biological tissue, the tissue components absorb the light and the tissue heats up slightly (less than 1°C).

This causes the tissue to expand and contract, creating vibrations, which can be picked up as ultrasonic sound waves by sensitive detectors.

Different materials and molecules inside the tissue absorb different amounts of the incident light at different wavelengths, creating individual ‘fingerprints’ in the emitted sound waves.

Importantly, this procedure does not damage the tissue sample being studied.

In the current study, the team exploited this approach to measure the concentration of a single molecule, namely glucose. They used polarised light – a light wave that oscillates only in a specific direction. Sunglasses, for example, reduce glare by blocking out light waves that oscillate in certain directions.

Glucose is a chiral molecule, which means that it has an inherent structural asymmetry that causes polarised light to rotate its orientation of oscillation when it interacts with the molecule.

The team found that the intensity of the emitted sound waves changed when the orientation of the polarised light interacting with glucose in the solution was changed.

“We don’t actually know why the acoustic signal changes when we change the polarisation state. But we can establish a relationship between the glucose concentration and the intensity of the acoustic signal at a particular wavelength,” said Jaya Prakash, Assistant Professor in IAP and corresponding author of the study published in Science Advances.

Glucose rotates the polarised light and the rotation increases with concentration, which is reflected in the acoustic signal intensity. Therefore, measuring the strength of the acoustic signal allowed the researchers to work backwards and estimate the concentration of glucose.

The researchers were able to estimate glucose concentration in water and serum solutions as well as slices of animal tissue with near clinical accuracy. They were also able to measure glucose concentration at various depths within the tissue accurately.

“If we know the speed of sound in this tissue, we can use the time series data to map our acoustic signals to the depth at which they are coming from,” explains Swathi Padmanabhan, PhD student and first author of the paper.

Since sound waves don’t scatter much inside tissue, the researchers were able to get accurate measurements at various tissue depths.